The present invention broadly relates to a novel aluminum alloy and novel continuously cast aluminum alloy casting thereof which may be cold worked to thin gauges without requiring a homogenizing thermal treatment. The invention further relates to a novel method of preparing semirigid container stock from the continuously cast aluminum alloy castings of the invention and to the novel container stock thus prepared.
Aluminum alloy semirigid container stock is widely used in the manufacture of disposable containers such as dishes, trays, pans, and cup-like articles for prepared fresh or frozen foods. The containers are usually manufactured with modern high speed equipment which stamps blanks from the container stock in sheet or strip form, and thereafter the blanks are shaped to a desired configuration in a hydraulic press.
Aluminum alloy container stock for the manufacture of semirigid disposable containers should have a combination of desirable properties if entirely satisfactory results are to be achieved. The thickness of the thin gauge aluminum sheet or strip should be about 0.001-0.01 inch and preferably about 0.002-0.008 inch to conserve metallic aluminum and thereby reduce material costs. At such thin gauges, it is essential that the container stock have relatively high tensile and yield strength so that the semirigid containers prepared therefrom will be sufficiently strong. The container stock also must be ductile and readily formable so that the blanks may be easily shaped in the hydraulic press.
The aluminum alloy most commonly used heretofore in preparing semirigid container stock meets the specifications of American Society for Metals (ASM) aluminum alloy specification 3003. This alloy contains 1.2% nominal manganese and the remainder aluminum, and it must be continuously or semi-continuously direct chill cast into an ingot having a thickness of several inches or more which is hot rolled and then cold rolled to the final thickness of about 0.001-0.01 inch. It is also essential that such alloy be subjected to a homogenizing thermal treatment at a minimum temperature of 850.degree.F. and usually at about 900.degree.-1000.degree.F. to control the undesirable effects of manganese, iron and/or silicon intermetallics. Because of the required hot rolling, the homogenizing thermal treatment must be conducted in a nonoxidizing atmosphere over a period of several hours and it adds very substantially to the cost of the product. Commercial operations employ the hot rolling step and the homogenizing thermal treatment and their elimination is not economically feasible.
In view of the foregoing, it is apparent that the prior art method of preparing semirigid container stock from aluminum alloy specification ASM 3003 requires an expensive hot rolling mill and a homogenizing thermal treatment which greatly increase the overall cost of the product. These costs could be reduced substantially by providing an aluminum alloy having the necessary properties for semirigid container stock capable of being cold rolled to a thickness of 0.001-0.01 inch without a homogenizing thermal treatment. The costs could be further reduced substantially by providing an aluminum alloy having the necessary properties for semirigid container stock which may be cast on a continuous strip caster to produce a 1/8 inch to 1 inch thick strip capable of being cold rolled to a thickness of 0.001 to 0.01 inch without a homogenizing thermal treatment to thus eliminate the requirement for a hot rolling mill and also the need for the costly prior art homogenizing thermal treatment.
Attempts have been made heretofore to continuously cast aluminum alloy specification ASM 3003 but it was not practical to homogenize the resulting continuously cast strip. Thus, the continuously cast strip could not be cold rolled to produce semirigid container stock having satisfactory properties. As a result, there has been a long standing need in this art for an aluminum alloy that may be continuously cast to provide castings which may be cold worked to thin gauges without requiring a homogenizing thermal treatment.
It is an object of the present invention to provide a novel aluminum alloy that may be continuously cast and cold worked to thin gauges without requiring a homogenizing thermal treatment.
It is a further object of the present invention to provide novel continuously cast aluminum alloy castings which may be cold worked to thin gauges without requiring a homogenizing thermal treatment.
It is a further object to provide novel continuously cast aluminum alloy castings that may be cold rolled without prior hot rolling and, in the absence of a homogenizing thermal treatment, to produce semirigid container stock having a thickness of about 0.001-0.01 inch.
It is a further object to provide a novel continuously cast aluminum alloy strip having a thickness not greater than about one inch which may be cold rolled in the absence of a homogenizing thermal treatment to produce semirigid container stock having a thickness of about 0.001-0.01 inch.
It is a further object to provide a method of preparing aluminum alloy semirigid container stock from the aforementioned continuously cast strip by cold rolling to the desired final thickness in the absence of a homogenizing thermal treatment.
It is a further object to provide the aluminum alloy semirigid container stock prepared by the aforementioned method of the invention.
Still other objects and advantages of the invention will be apparent to those skilled in the art upon reference to the following detailed description and the specific examples.